1. Field of the Invention
The present invention relates to a method of mounting a semiconductor chip on a surface of a solid device with a face-down posture to produce a semiconductor device.
2. Description of Related Art
Known as a method of mounting a semiconductor chip on another semiconductor chip or a wiring board has been a face-down method for opposing and joining a surface of a semiconductor chip to a surface of a solid device such as another semiconductor chip or a wiring board.
On the surface of the semiconductor chip to be mounted by the face-down method, metal electrode portions called bumps are formed in a raised state. On the other hand, on the surface of the other semiconductor chip or the wiring board as a base, bumps are also formed at positions corresponding to the bumps formed on the semiconductor chip to be mounted. In mounting the semiconductor chip on the other semiconductor chip or the wiring board as the base, an anisotropic conductive film is interposed between the semiconductor chip and the semiconductor chip or the wiring board as the base. Thereafter, the bumps on the semiconductor chip and the bumps, which are opposed thereto, on the semiconductor chip or the wiring board as the base are pressed against each other.
The anisotropic conductive film has a structure in which conductive particles are dispersed in a resin film having adhesive properties. When the bumps which are opposed to each other with the anisotropic conductive film interposed therebetween are pressed against each other, therefore, the anisotropic conductive film is crushed between the bumps. Consequently, the bumps are bonded to each other by the resin film having adhesive properties, and conductive particles are sandwiched between the bumps, thereby achieving electrical connection between the bumps.
However, it takes relatively long for the anisotropic conductive film to be crushed between the opposed bumps, exhibiting the adhesive properties of the resin film in the anisotropic conductive film. Therefore, it takes relatively long for the step of mounting the semiconductor chip using the anisotropic conductive film.
When gold is used as a material for the bumps, it is considered that the bumps on the semiconductor chip and the bumps, which are opposed thereto, on the semiconductor chip or the wiring board as the base can be bonded to each other by being directly abutted and pressed against each other even if the anisotropic conductive film is not used. Consequently, it is possible to shorten time required for the step of mounting the semiconductor chip.
In this method, however, the opposed bumps may not be satisfactorily joined to each other if the surfaces of the bumps (a joint surface between the bumps) are dirty because an impurity layer adheres thereto.
An object of the present invention is to provide a method of producing a semiconductor device, which makes it possible to shorten time required for the step of producing the semiconductor device and to reliably bond a metal electrode portion on a semiconductor chip and a metal electrode portion on a solid device to each other.
The present invention relates to a method of opposing and joining a surface of a semiconductor chip to a surface of a solid device to produce a semiconductor device. The method according to the present invention comprises the steps of directly abutting and pressing a metal electrode portion formed in a raised state on the surface of the solid device and a metal electrode portion formed in a raised state on the surface of the semiconductor chip; and transmitting ultrasonic vibration to the metal electrode portions which are pressed against each other.
The solid device may be a semiconductor chip other than the semiconductor chip or a wiring board.
It is preferable that both the metal electrode portions which are respectively formed in a raised state on the surfaces of the solid device and the semiconductor chip are bumps composed of gold.
According to the present invention, the metal electrode portion formed on the surface of the semiconductor chip and the metal electrode portion formed on the surface of the solid device are bonded to each other by transmitting the ultrasonic vibration to a portion between the metal electrode portion on the semiconductor chip and the metal electrode portion on the solid device while pressing the metal electrode portions against each other.
When the metal electrode portion on the semiconductor chip and the metal electrode portion on the solid device are bonded to each other with an anisotropic conductive film interposed between the semiconductor chip and the solid device by the adhesive properties of the anisotropic conductive film, it takes approximately 20 seconds for the bonding. Contrary to this, in the method according to the present invention, when both the metal electrode portion on the semiconductor chip and the metal electrode portion on the solid device are composed of gold, time required to bond the metal electrode portion on the semiconductor chip and the metal electrode portion on the solid device is relatively short, for example, approximately 0.2 seconds. In the method according to the present invention, therefore, time required to produce the semiconductor device can be made shorter, as compared with that in the method of bonding the semiconductor chip and the solid device using the anisotropic conductive film.
Even if an impurity layer adheres to the surfaces of the metal electrode portions, the adhering impurity layer is torn by the transmission of the ultrasonic vibration. Consequently, metal atoms composing the metal electrode portions can be satisfactorily diffused between the metal electrode portions. Accordingly, it is possible to reliably bond the metal electrode portion on the semiconductor chip and the metal electrode portion on the solid device.
The ultrasonic vibration may be inputted to the semiconductor chip or the solid device. The ultrasonic vibration which has been inputted to the semiconductor chip or the solid device reaches a joint surface between the metal electrode portion on the semiconductor chip and the metal electrode portion on the solid device upon propagating through the semiconductor chip or the solid device.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.